Comparison of Six Radiographic Projections to Assess Femoral Head/Neck Asphericity

Abstract

Early radiographic detection of femoroacetabular impingement might prevent initiation and progression of osteoarthritis. The structural abnormality in femoral-induced femoroacetabular impingement (cam type) is frequently asphericity at the anterosuperior head/neck contour. To determine which of six radiographic projections (anteroposterior, Dunn, Dunn/45° flexion, cross-table/15° internal rotation, cross-table/neutral rotation, and cross-table/15° external rotation) best identifies femoral head/neck asphericity, we studied 21 desiccated femurs; 11 with an aspherical femoral head/neck contour and 10 with a spherical femoral head/neck contour. To radiographically quantify femoral head asphericity, we measured the angle where the femoral head/neck leaves sphericity (angle alpha). The aspherical femoral head/neck contours had a greater maximum angle alpha (70°) compared with the spherical head/neck contours (50°). The angle alpha varied depending on the radiographic projection: it was greatest in the Dunn view with 45° hip flexion (71° ± 10°) and least in the cross-table view in 15° external rotation (51° ± 7°). Diagnosis of a pathologic femoral head/neck contour depends on the radiologic projection. The Dunn view in 45° or 90° flexion or a cross-table projection in internal rotation best show femoral head/neck asphericity, whereas anteroposterior or externally rotated cross-table views are likely to miss asphericity. Level of Evidence: Prognostic study, level II-1 (retrospective study). See the Guidelines for Authors for a complete description of levels of evidence.